This invention relates to bearings for rotary support of rotating cutting tools and more particularly for bearings used to support the cutting tool in surgical drill motors and/or attachments therefor.
The following patent applications, contemporaneously filed with this patent application and assigned to the same assignee relate to the subject matter of this patent application and are incorporated herein by reference. They include the patent application Ser. No. 09/962,461 entitled xe2x80x9cMiniature Cutter Shaft Configurationxe2x80x9d filed by Eddy H. Del Rio, Douglas Perry, Jose M. Lamanna, and Thomas D. Anspach and the patent application Ser. No. 09/962,957 entitled xe2x80x9cMiniature Clutch for High Speed Surgical Drillsxe2x80x9d filed by Eddy H. Del Rio, Douglas A. Perry, Jose M. Lamanna and Thomas D. Anspach.
As one skilled in the medical technological field appreciates, the surgeon that uses surgical drills for performing surgery on a patient and particularly, in the neurological arena, requires that the instruments have a satisfactory xe2x80x9cfeelxe2x80x9d and xe2x80x9cvisual efficacyxe2x80x9d. In other words, the surgeon needs to feel not only confident in the quality and efficacy of the surgical instrument being used, that the tool has structural integrity and reliance, he would also like to be capable of seeing what is happening where the cutting is taking place. Obviously, ball bearings are typically used for high speed rotary types of instruments because they afford low friction and satisfactory rotary support. However, because the ball bearings require inner and outer races in addition to the balls, the envelope to house these bearings is typically large. For example, the diameter of the working end (distal end) of surgical drills with or without adapters are at a minimum equal to 5-7 millimeters. Although the cutting tool projects a small axial distance from the end of the drill/adapter, which is dictated by structural integrity, bending loads, etc., this diameter of the support mechanism at the distal end of the instrument impedes the line of sight of the surgeon while working within the patient""s cavity. This invention constitutes an improvement over the mechanism disclosed in U.S. Pat. No. 5,405,348 granted on Apr. 11, 1995 to William E. Anspach, Jr. and Eddy H. Del Rio, a joint inventor of this patent application, entitled xe2x80x9cSurgical Cutting Instrumentxe2x80x9d. In the positive bearing in the support tube for supporting the shaft of the cutter, the support tube is configured into a triangular shape and carries three circumferentially disposed lands made from a low coefficient of friction and high density material. It is apparent merely from a visual inspection of this bearing, that it is more complicated to fabricate this type of bearing construction, since the bearing plates require retaining means to hold them into the desired position. Whereas, the journal bearing of this invention, merely requires insertion into the tube without anything further. Also, the bearing disclosed in the U.S. Pat. No. 5,405,348 patent, supra, requires lubrication and cooling for the bearing or it would otherwise fail instantly or substantially instantly. The inventive bearing described hereinbelow does not require lubrication and/or cooling.
We have found that by judiciously configuring the bearing and making the bearing out of a given polyimide material, we can significantly reduce the bearing size without sacrificing speed, integrity and reliability, with a consequential reduction in the size of the envelope where the bearing are housed and likewise, obtain a consequential reduction in the outer diameter of the instrument at the distal end. Hence, the overall diameter of the distal end is made sufficiently small to overcome the visual problems evidenced in heretofore known surgical instruments of this type. We have found that we can reduce the outer diameter by 50% or more.
In addition, since the cutting tool is made to be removably inserted into the motor or adapter, it is necessary to assure that the shaft of the tool bit is inserted through the bearings with ease and without being cumbersome to install. To this end, the intermediate bearings, i.e. the bearings out of sight of the operator are judiciously countersunk to define a ramp that serves to guide the shaft into and/or through the bearing.
An object of this invention is to provide an improved bearing for a surgical instrument that reduces the overall diameter size of the surgical instrument and enhances the line of sight for the surgeon.
A feature of this invention is to configure the inner diameter of the bearing in a substantially square configuration in cross section and to make the bearing out of a polyimide resin material. The size of the bearing and shaft is predicated on there being a point contact during the operating envelope of the surgical drill or the attachment. Other cross sectional configurations, other than circular, can be utilized so long as these configurations have the two point contact during the rotational envelope of the drill or attachment.
A still further feature is to use a polyimide resin and carbon/graphite material for the bearing.
A still further feature is to make the bearing from VESPEL (a product of the Dupont Company) SP-22 or SP-21 material.
Another feature of the invention is to contour the inlet side of the bearing to guide the shank of the tool bit into and through the bearing.
The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings.